Anyone know a way to confirm if my stock 1985 Temp Gauge is reading/operating accurately without hooking up a separate new aftermarket gauge to confirm? For instance running certain voltages through the stat to make it read specific temperatures? I'm pretty sure it's reading high but don't want to be overheating... Thanks!

 

Thermostats don't have voltage...

 

Or ohms?

 

Nope, they don't have ohms either...

 

Right on, super helpful. Always thought single wire temp sensors report resistance back to the gauge.

Anyone else have any input here?
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You said "thermostat". That's not a thermostat. And a sensor doesn't report to the gauge. It reports to the ECM.
Kind'a hard to help someone when they are not clear on what they want help with.

Your SENDING UNIT is probably fine. The factory gauge is notoriously inaccurate...

 

Ahh, I see the miscommunication. I should have said Temperature gauge, not thermostat. So that being said, is this likely just a bad gauge and a new one will fix it or are they all inaccurate due to inherent issues with the ECM and/or design of the temperature reading system in whole?

 

Well I don't think "new" ones are available, but I wouldn't be surprised if most of them are 5° to 10° off. The ECM has nothing to do with your gauge reading. It reads from the sending unit in the driver-side cylinder head.
I would suggest getting one of these to compare your gauge accuracy:
https://www.ebay.com/itm/12416135229...BlBMULj9mNuWYw

 

Third gen temp gauges aren't nearly accurate enough to provide an absolute temperature measurement. If your panel gauge moves at all as the engine warms up, its value is in using it for relative readings. IOW, if you see it reporting higher/lower than where it normally reads, you might have a problem.

As T.L. posted above, get yourself an IR gun and use it to relate what your temp gauge reads to what the engine is actually doing.

 

The Shop manual covers the procedure for testing individual gauges by using Kent Moore J-24538-A Universal Gauge Tester .

https://www.ebay.com/itm/26643899077...Bk9SR_aVkPKWYw


Both things are prone to inaccurate readings; Every temp sending unit and every actual Temp Gauge. IMO the best way to judge accuracy is to do 2 things: find out when the thermostat opens and note the displayed temp; and find out when it overheats and note the displayed temp.

When you install a Thermostat it's marked with it's temp rating. When you KNOW it's temp rating simply start the car and hold the upper hose till you feel the thermostat open - it quickly gets real hot - and compare it to the displayed temp. You can obtain a good idea how far off the temp reading is based on this test/check.

If you test the coolant in the car you can find it's Boil Point. Then unplug the fan ( or remove clutch fan ), start the car and let it idle till it starts to overheat and kill the engine AS SOON AS you see coolant flow into the overflow.bottle and make note of the temp displayed compared to the coolant boil rating. This will verify that your coolant is mixed properly - but more important it will tell you what reading ( accurate or not ) on the temp gauge means your going to overheat.

** The last time I flushed my radiator I was also setting the secondary fan temp operation at the time and recall that I swapped 3-4 different temp sending units during repeated flushing and each of the sending units caused a slightly different reading on the gauge. I ended up using the sending unit that showed the closet reading to 180 (based on the Thermostat opening) and was lucky in that it was also the closest to the correct boil-over reading.

 

Thanks for the responses guys. This is a really good way to find out exactly how the stat is operating and compare it to the gauge readings. I'm actually not running a stat currently so I'll go ahead and buy the IR reader and run some comparisons! Thanks for your help!

 

The engine requires a thermostat to run properly; engine temp is one of the factors the computer reads.